Camphor has a strong, penetrating smell that mice can detect at extremely low concentrations, but there is no solid scientific evidence that it reliably repels them from your home. While camphor does irritate rodent airways and taste buds, the effect is temporary and fades as the substance evaporates. Most pest control professionals do not recommend it as a standalone solution for a mouse problem.
What the Research Actually Shows
The most relevant published research on camphor and rodents tested camphor oil not as a repellent, but as a poison mixed into food and water. In a study published in the Open Veterinary Journal, Norway rats given camphor oil at a 10% concentration in their water supply showed reduced water intake on the first day of exposure, drinking as little as 7.5 ml compared to normal amounts. That initial avoidance is the closest thing to a “repellent effect” in the scientific literature.
But here’s the important part: the rats didn’t stay away. Over the 21-day experiment, 40% of the rats died from ingesting camphor oil at that highest concentration, meaning the majority continued consuming it despite the unpleasant taste and toxic effects. If rats won’t reliably avoid camphor when it’s mixed directly into their water, scattering camphor tablets or mothballs around your basement is unlikely to drive them out.
Why Mice Can Smell It So Strongly
Rats and mice do have a powerful biological response to camphor. Research on the rat olfactory system found that receptors in the nasal lining bind to camphor molecules with extremely high sensitivity. These receptors are specialized proteins embedded in the tissue of the nasal passages, and they lock onto camphor at concentrations far below what humans can detect. That’s why you might see a mouse initially startle or avoid an area where you’ve placed fresh camphor.
The problem is that this response doesn’t last. Camphor is a volatile compound, meaning it evaporates into the air relatively quickly. As it dissipates, the concentration drops below the threshold that bothers rodents. In an open room, a crawl space, or an attic with any airflow, camphor tablets lose their potency within days. Mice are also highly adaptable. Once they associate a smell with a food source or nesting area, they learn to tolerate it.
Real Risks of Using Camphor Indoors
Camphor poses safety concerns that outweigh its questionable repellent value, particularly in homes with children or pets. The neurotoxic dose for humans is roughly 50 mg per kilogram of body weight, and for a small child, that can mean just a few tablets. Seizures are the most common serious symptom of camphor ingestion, sometimes appearing as the very first sign of poisoning. Other symptoms include nausea, vomiting, abdominal pain, and a strong chemical smell on the breath. The fatal dose is estimated at 500 mg per kilogram, but children have experienced life-threatening reactions at much lower amounts. The FDA restricts camphor concentration in consumer products to under 11% for this reason.
Inhaling camphor fumes in enclosed spaces also carries risks. Workers exposed to airborne camphor concentrations during manufacturing reported nose and sinus irritation, eye irritation, and drowsiness. If you’re placing camphor in a small closet, pantry, or sealed attic space where the fumes concentrate, you could experience similar symptoms over time. Camphor is also flammable, with a flash point of 150°F. Placing it near heat sources, electrical outlets, or in a hot attic during summer creates a real fire hazard.
Why Mice Ignore Most “Natural” Repellents
Camphor falls into the same category as peppermint oil, mothballs, dryer sheets, and dozens of other home remedies that people try before calling an exterminator. The pattern is the same for nearly all of them: the strong scent causes brief avoidance, the smell fades or the mice habituate, and the infestation continues. Mice are driven by survival needs (food, water, shelter, warmth) that easily override an unpleasant odor, especially once they’ve established a nest.
A mouse can squeeze through a gap the width of a pencil. If your home offers reliable food scraps, pet food, or warmth during cold months, no scent barrier will override that motivation. The mice may simply find a different entry point that avoids the camphor entirely.
What Works Better
Effective mouse control comes down to three things: sealing entry points, removing food sources, and trapping. Steel wool packed into gaps around pipes, foundation cracks, and utility line entries is one of the most effective physical barriers because mice can’t chew through it easily. Combining steel wool with caulk creates a durable seal.
Inside, store all food (including pet food and birdseed) in hard-sided containers with tight lids. Clean up crumbs and spills promptly, and don’t leave dirty dishes in the sink overnight. Snap traps placed along walls where you’ve noticed droppings remain the most reliable way to reduce an active mouse population. Place them perpendicular to the wall with the trigger end facing the baseboard, since mice tend to run along edges rather than through open spaces.
For serious infestations, especially in older homes with many potential entry points, a professional pest control service can identify and seal gaps you might miss and deploy bait stations in locations that are safe from children and pets. This approach addresses the root problem rather than masking it with a scent that mice will eventually ignore.